Microtome blade holder

ABSTRACT

A holder for rigidly mounting a conventional razor blade on a microtome, the blade being adhesively secured to the holder on a precisely ground mounting face defined downwardly by an upwardly directed shoulder and an undercut groove. Assembly of a blade on the holder is accomplished by first coating one face of the blade and the mounting face of the holder with a flowable adhesive such as cyano acrylate polymerizing cement, then pressing the coated face of the blade against the upper edge of the holder, then pivoting the blade about that line into full contact with the mounting face, thus squeezing excess adhesive downwardly into the undercut groove, and finally sliding the blade downwardly so that its base bottoms against the shoulder. The shoulder must be sufficiently shallow to insure that no portion of the shoulder is exposed when the blade is mounted thereon, so that no obstruction impedes the downward sliding movement of a tissue section. Removal of a used blade is accomplished by inserting a pointed tool into the groove and prying the blade away from the holder.

United States Patent 91 Taylor et a1.

[451 Apr. 17, 1973 MICROTOME BLADE HOLDER [76] Inventors: Dermot B.Taylor, 3914 Sierks Way, Malibu, Calif. 90265; Daniel C. Pease, 13011Sunset Boulevard, Los Angeles, Calif. 90049 [22] Filed: May 6,1971

21 App]. No.: 140,678

Primary Examiner-Andrew R. Juhasz Assistant ExamirierW. D. BrayAttorneyMiketta, Glenny, Poms & Smith ABS'I RACT A holder for rigidlymounting a conventional razor blade on a microtome, the blade beingadhesively secured to the holder on a precisely ground mounting facedefined downwardly by an upwardly directed shoulder and an undercutgroove. Assembly of a blade on the holder is accomplished by firstcoating one face of the blade and the mounting face of the holder with aflowable adhesive such as cyano acrylate polymerizing cement, thenpressing the coated face of the blade against the upper edge of theholder, then pivoting the blade about that line into full contact withthe mounting face, thus squeezing excess adhesive downwardly into theundercut groove, and finally sliding the blade downwardly so that itsbase bottoms against the shoulder. The shoulder must be sufficientlyshallow to insure that no portion of the shoulder is exposed when theblade is mounted thereon, so that no obstruction impedes the downwardsliding movement of a tissue section. Removal of a used blade isaccomplished by inserting a pointed tool into the groove and prying theblade away from the holder.

3 Clailm, 6 Drawing Figures MICROTOME BLADE HOLDER BACKGROUND ANDSUMMARY OF THE INVENTION:

This invention relates generally to razor or similar disposable bladeholders, and more particularly to such a holder especially adapted formounting razor blades in a microtome or similar precision cuttinginstrument.

Microtomes are machine tools extensively used for cutting thin sectionsof animal or vegetable tissue for microscopic examination in clinicalpathology, in medical research, and other medial areas. The sections,typically only a few microns in thickness, are usually sliced from ablock of tissue which has been frozen or plasticized for rigidity. Theproblems presented in the design and use of knives in these machines aredifferent from and generally much more severe than those which occur inother fields, such as surgical knives and the like.

In a microtome, a block of biological tissue, usually either frozen orembedded in wax or plastic, is moved past an accurately positionedcutting edge, and a very thin section of the tissue is sliced from theblock. This section of tissue, typically less than microns in thickness,must slide smoothly across the front surface of the knife in order toprevent its being deformed or torn. After the cut is completed andbefore the next stroke, the block of tissue is advanced mechanically bya precise distance, equal to the thickness of the section to be cut. Theblock of tissue is then again moved past the cutting edge and anothersection is cut therefrom. The thickness of the section and the cleannessand uniformity of the slicing action quite clearly depend upon theaccurate positioning and sharpness of the knife used.

The conventional microtome knife is a rigid slab of special steel,approximately 4 to 10 inches long and of a wed ge-shaped cross section,the apex of the wedge constituting the cutting edge and being directedgenerally upwardly. The knife is held in the microtome in an inclinedposition so that its center line is about 30 to the plane of movement ofthe tissue. The frozen or plasticized tissue, cut by the knife, has manyof the characteristics of a solid block of ice, and the force exerted oncutting edge of the microtome knife by the tissue block is considerable.Therefore the knife must have sufficient rigidity to resist this force.Not only must the cutting edge of the knife resist this force but itmust not deflect while so resisting. If the knife edge is deflected bythe cutting force, the section may not have a uniform thickness andhence may be unusable.

Clearly then the knife for a microtome must be extraordinarily rigid andmaintain its shape and position within very close tolerances despitebeing subjected to considerable force on its cutting edge. Moreover,with such a fine cut, the cutting edge of the microtome knife must beuniform, straight and as sharp as it is possible to achieve. Thesespecific requirements are unique to knives for use in microtomes, andhence knives suitable for other applications are not suitable for use inmicrotomes.

The major problem presented by a conventional microtome knife issharpness. Conventional microtome knives are made as sharp as possible,but this sharpness heretofore has not approached the sharpness attainedby a conventional razor blade. The reasons for this lack of sharpnessare primarily economic, i.e. there is not enough demand for microtomeknives to justify spending the money required for research andproduction of a resharpenable microtome knife which would be as sharp asa modern razor blade.

Not only are microtome knives not as sharp as razor blades, but after afew cutting strokes in a microtome, the sharpness of a microtome knifeis reduced. Eventually the cutting edge of the microtome knife becomesso dull or nicked that the knife is unusable and then the blade must beresharpened. Current medical practice is to purchase a specially mademicrotome knife together with a complex and expensive machine to sharpenthe microtome knives. Even with such equipment the cutting edge achieveddoes not approach in sharpness the edge on a modern razor bladeavailable through conventional sales outlets.

Another advantage of the razor blade is that it typically has a coatingof plastic which facilitates movement of a tissue section past thecutting edge.

Therefore it is desirable to use a commercially made razor blade as thecutting edge in a microtome knife and thereby utilize the sharpness ofthe razor blade to cleanly cut thin tissue sections. However, there aremany problems presented by such an improvement before it would bepractical. One problem is presented by the flexibility of a razor blade.Another problem associated with the use of a razor blade in a microtomeis the accurate positioning of the razor blade relative to the plane ofmovement of the tissue block.

The principal object of this invention is to provide a novel holder formounting a razor blade in a microtome or the like.

Other and additional objects of this invention are to provide such ablade holder which will rigidly support the razor blade subjected to theforces required to cut a frozen or plasticized block of tissue; toprovide a blade holder which will locate the razor blade with therequired accuracy to cut a thin slice of tissue from a frozen orplasticized block; to provide a blade holder which supports the bladealong its surface to prevent the blade from buckling and breaking away;to provide a blade holder with a blade thereon, which provides a smoothupper surface over which the thin sections of frozen or plasticizedtissue may move after being cut; to provide a blade holder which willaccurately align the cutting edge of the razor blade thereon withrespect to the frozen block; to provide a blade holder which willaccurately align more than one razor blade thereon; to provide such ablade holder from which the razor blades can be easily removed when theybecome dull, and to which replacement blades can be mounted; and toprovide such a blade holder which is inexpensive to manufacture, adaptedfor use in existing microtomes, and which is easy and convenient for atechnician to use.

The present blade holder is generally V-shaped in section with its apexdirected generally upwardly. Its front surface is inclined forwardlyfrom the plane of tissue movement by approximately 30, and its rearsurface is inclined to that plane by about 10 or less. Thus the apexangle of the holder may be 20 or thereabouts.

The front surface of the holder includes a precisely ground mountingface extending downwardly from the upper edge or apex, and defineddownwardly by an undercut groove and an upwardly directed shoulder, boththe groove and shoulder being parallel to the apex.

Thus the mounting face is recessed rearwardly from the front surface ofthe holder by the depth of the shoulder. That depth is desirably equalto or slightly less than the thickness of the razor blade to be mountedthereon. In any event, no portion of the shoulder may be permitted to beexposed when the razor blade is in its operative position. As will beunderstood, the exposed portion of the shoulder would then constitute apartial obstruction to the smooth downward sliding movement of a tissuesection, and might deform or tear the section.

In assembling a blade on the holder, the operator first coats one faceof the clean blade and the mounting face of the holder with a flowableadhesive such as cyano acrylate polymerizing cement and then presses thecoated face of the blade against the upper edge of the holder, with theblade cutting edge projecting slightly above the holder apex. Theoperator then pivots the blade about the apex into full contact with themounting face, thus squeezing any excess adhesive downwardly into theundercut groove. Finally the operator slides the blade downwardly sothat its lower edge of base bottoms against the shoulder. For maximumrigidity of the blade cutting edge, it is essential that the distancebetween the apex and shoulder be virtually equal to the distance betweenthe base edge of the blade and the beginning of the bevel of the bladecutting edge.

After a blade has become too dull for further use, the

operator can easily remove it from the holder by inserting a pointedtool in the undercut groove of the holder and then prying the bladeloose from its adhesive attachment to the holder mounting face. Anyadhesive remaining on the holder should of course then be removed by asuitable solvent such as nitromethane, dimethylsulfoxide ordimethylformamide, before a new blade is mounted thereon. The inventionwill be better understood from a reading of the following description ofa preferred embodiment of the invention, taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of asimple microtome having mounted thereon a holder in accordance with thepresent invention; in dotted outline there is shown an illustrative pathof movement of a tissue section after being cut, together with the handsof an operator.

FIG. 2 is an elevational view on an enlarged scale of the holder havingmounted thereon a razor blade in accordance with the present inventionand, fragmentarily shown, two adjacent blades mounted on the holder.

FIG. 3 is a sectional view on a greatly enlarged scale taken on arrowsIII-III of FIG. 2.

FIG. 4 is a sectional view similar to FIG. 3, but showing therelationship of a razor blade and the holder during assembly.

FIG. 5 is a view of a conventional double edged razor blade, showingcuts which may be made in order to adapt one-half of the complete bladefor use in accordance with the present invention.

FIG. 6 is a fragmentary view, similar to FIG. 2, showing a used bladebeing removed from the holder.

DETAILED DESCRIPTION Referring now to the drawing, in FIG. 1 there isindicated generally a simple microtome operated by hand having mountedthereon a holder in accordance with the present invention. As will beunderstood, the particular design of the microtome is immaterial to thepresent invention, which is applicable to virtually all microtomespresently used. The holder in accordance with the present invention isindicated generally at 12 and is desirably made of strong rigid materialsuch as steel. The holder may be of any suitable length, illustrativelyabout 6 inches. Holder 12 has mounted thereon a razor blade indicatedgenerally at 14, and a typcial path of movement of a tissue sectionafter being cut is shown in dotted outline at 16.

In FIG. 2 there is shown, on an enlarged scale, a portion of holder 12having mounted thereon blade 14 as well as, fragmentarily shown,adjacent blades 18 and 19.

As will be understood by reference to FIG. 3, holder 12 is generallywedge-shaped as seen in section, having a rear wall 20 and a front wall21. In the upper portion of the holder there is formed a-precisionmounting face 22, recessed from the plane of wall 21 and desirablyparallel thereto. Mounting face 22 and rear wall 20 join upwardly atupper edge or apex 25. Angle A of apex 25 is desirably about 20. Theplane of movement or travel of the tissue block being cut is indicatedat 26, and rear wall 20 of the holder is inclined forwardly from thatplane by an angle B, which may be approximately 10.

Precision mounting face 22 is defined downwardly by an undercut grooveindicated generally at 30, here shown as semicircular in profile,although the groove may assume any other convenient shape. Groove 30terminates downwardly in a shoulder 32 which is perpendicular to theplane of mounting face 22. Blade 14 is mounted on holder 12, having itscutting edge 34 directed generally upwardly, and its lower wall or base36 bottomed against shoulder 32. The blade is retained in position by acoating of adhesive 38. When the adhesive used in retaining the bladeand holder in assembled relation is flowable, as is presently preferred,it is important to minimize, and preferably to eliminate, thepossibility that some of the excess adhesive will flow upwardly as seenin FIG. 3 beyond apex 25 of the holder. If such adhesive does flow inthat direction, it would harm the tissue block during its downwardmovement while a section is being cut. In FIG. 4 there is shown a stepin assembly of the blade and holder in order to minimize leakage of theadhesive upwardly around apex 25. Thus, a coating of adhesive 38 isapplied to the precision mounting face 22 of the holder. A small amountof adhesive may also be applied to the rear face of blade 14, but suchapplication of adhesive to the blade itself should be primarily in thelower portion of the blade as seen in FIG. 4. The blade is then pressedagainst the apex, and the blade is then pivoted about the apex as afulcrum, maintaining a tight line of contact between the blade and theapex, and thereby preventing adhesive from flowing upwardly beyond theapex. Thus the entire face of the blade is swung into contact withadhesive 38 on the mounting face 22, and in FIG. 4, in dotted outline,there is shown the lower portion of the blade after being so swung. Theblade is then moved downwardly so that its base 36 bottoms against theshoulder 32, as seen in the completely assembled view FIG. 3. It is tobe noted that, during the swinging movement just referred to, as well asthe downward sliding movement into the position of FIG. 3, a certainamount of excess adhesive will be forced downwardly along face 22, andwill be received in the undercut groove 30. The groove thus serves ineffect as a sump, and prevents the possibility that adhesive may flowonto shoulder 32 where it would form a sticky deposit difficult to cleanoff.

Ideally shoulder 32 is made to be precisely prependicular to the planeof the precision mounting face 22. It is important that the includedangle forming shoulder 32 be not an obtuse angle. If any tolerance ispermitted in the manufacture, it must be in the direction to make theincluded angle acute, for example 88 or 89. As will be understood, ifthe included angle of shoulder 32 were greater than 90, there would bean inaccurate bottoming of blade 14 on the holder.

With particular reference to the upper portion of FIG. 3, in the regionof apex 25, it will be seen that, as is conventional, the upper endportion of blade 14 is beveled at 40 to the cutting edge 34. For maximumstrength and rigidity of the assembly, apex should be as close aspossible to the base of bevel 40.

The razor blade to be used in accordance with the present invention maybe of the single edge injector type; or, preferably, one-half of aconventional double edged blade. Such a double edged blade is shown inFIG. 5, including an upper portion indicated generally at 14, the bladepreviously referred to in the above description. Similarly, the bladeincludes an identical lower portion indicated generally at 45, the twoblade portions being symmetrically disposed about the longitudinalcenter line of the complete blade. End portions 46 and 47 of the blademay be cut or broken off, in order to convert the double edged bladeinto a pair of blades usable in accordance with the present invention.

Removal of a used blade is easily accomplished in accordance with thepresent invention. As shown in FIG. 6, the undercut groove of holder 12is sized to receive the end of a small tool, indicated generally at 50,the end portion 51 desirably constituting a hook and thus serving topull the blade loose from its adhesive mounting on holder 12. The bladethus removed is of course discarded. After removal of a used blade, theholder, and particularly the precision mounting face 22, is cleaned ofany remaining adhesive by suitable solvent means.

A typical adhesive usable in the present invention is cyano acrylatcpolymerizing cement, and a solvent for removal of excess or remainingadhesive after removal ofa used blade may be, for example, nitromethane.

Groove 30 not only serves as a sump as discussed above, but isadditionally advantageous during manufacture of the holder in insuringthat the blade will be positioned as exactly as possible in its properposition on the holder. As previously pointed out, apex 25 must be asnearly as possible exactly aligned with the base of bevel on the bladefor maximum rigidity of the assembly. If no groove were used, and if theprecision mounting face 22 and indexing shoulder 32 were formed by asingle grinding operation, several problems arise which would seriouslymilitate against the desideratum of accurate alignment of apex 25 withthe base of bevel 40.

Two of the major problems, discussed in detail below, are summarized asfollows:

1. Maintaining true planarity of indexing shoulder 32 intersecting theplane of mounting face 22 at a sharp right angle.

2. Accurately controlling the distance from indexing shoulder 32 to apex25.

With reference to maintaining true planarity of shoulder 32, it will beunderstood that the use of a grinding wheel or similar movable abrasivemember to form precision mounting face 22 would inevitably fail to forma sharp interior right angle at the intersection of face 22 and shoulder32. Wear on the grinding wheel edge would produce a curved contour ofthat intersection, preventing accurate bottoming of the base of therazor blade on the shoulder.

With reference to the accurate control of the distance from indexingshoulder 32 to apex 25, it will be evident that the process of grindingor otherwise forming the precision mounting face 22 produces a shiftdownwardly of apex 25 by a distance several times greater than the depthby which the mounting face'22 is recessed from the plane of front wall21 of the holder. Specifically, the downward shift of apex 25 will beequal to the cotangent of angle A multiplied by such recessed depth. Ifangle A assumes the preferred value of 20, cot A 2.75, and the downwardshift of the apex will thus be almost 3 times the recessed depth. By thesame token, and more important for present purposes, variations in theapex downward shift from nominal will similarly be almost 3 times thevariations from nominal of the recess depth. Thus the tolerance of therecessed depth would have to be about one-third of what would otherwisebe permissible in order to maintain the distance from apex 25 toshoulder 32 within acceptable limits of accuracy.

Modifications and changes from the illustrative forms and dimensionshereinabove described and illustrated are within the contemplation ofthe invention, and are intended to be embraced within the scope of theappended claims.

We claim:

1. A holder for rigidly mounting a razor balde in a microtome or thelike, said blade having a cutting edge and a base edge parallel to thecutting edge, comprisa block of strong rigid material, wedge shapedinsection, having an upper apex edge, the front surface downwardly fromthe edge constituting a planar mounting face defined downwardly by anundercut groove terminating in an upwardly directed shoulder projectingforwardly from the plane of the mounting face by a distance no greaterthan the thickness of a razor blade to be mounted thereon, the grooveand shoulder being parallel to the apex edge.

2. The invention as defined in claim 1 wherein the shoulder lies in aplane perpendicular to the mounting face.

3. The invention as defined in claim 2 wherein thedistance from theplane of said shoulder to the apex edge is slightly less than the depthof a blade to be mounted thereon, whereby the blade cutting edgeprojects only slightly above the apex edge when the razor base is inabutting contact with the shoulder.

1. A holder for rigidly mounting a razor blade in a microtome or thelike, said blade having a cutting edge and a base edge parallel to thecutting edge, comprising: a block of strong rigid material, wedge shapedin section, having an upper apex edge, the front surface downwardly fromthe edge constituting a planar mounting face defined downwardly by anundercut groove terminating in an upwardly directed shoulder projectingforwardly from the plane of the mounting face by a distance no greaterthan the thickness of a razor blade to be mounted thereon, the grooveand shoulder being parallel to the apex edge.
 2. The invention asdefined in claim 1 wherein the shoulder lies in a plane perpendicular tothe mounting face.
 3. The invention as defined in claim 2 wherein thedistance from the plane of said shoulder to the apex edge is slightlyless than the depth of a blade to be mounted thereon, whereby the bladecutting edge projects only slightly above the apex edge when the razorbase is in abutting contact with the shoulder.